In water-based cleaning, significant energy is required for pre-treating and heating up cleaning water, operating high-pressure pumps, drying parts as well as treating wastewater.
Compared to the higher volatility of solvents, water is a slow-drying cleaner and requires more elaborated drying procedures aided by heaters or blowers. Water requires 10 times more of the latent heat of vaporization (2259 J/g) than that of solvents, which lie typically between 200-300 J/g.
Solvent vapor degreasing also requires energy to keep the entire operation under vacuum condition. As operating temperatures are reduced accordingly in a vacuum, the boiling point of solvent is also reduced, making evaporation quick and effective.
Vapor degreasing systems usually work vertically, compared to aqueous cleaning which often operates horizontally (a typical aqueous batch system may have one wash tank and 2-5 rinse tanks, with the number of rinse tanks depending upon the required cleaning quality). Water-based cleaning therefore tends to require a larger footprint (and more electricity to run). The humidity and heat generated by the aqueous cleaning system also needs to be counteracted by the air conditioning system, another energy cost factor that should be considered.